Scroll type compressors with one fixed scroll and one orbital scroll are used to compress refrigerant in mobile air conditioning systems. These compressors include a housing with a fluid inlet and a fluid outlet. A fixed scroll and an orbital scroll are positioned inside the housing. A drive assembly is provided to drive the orbital scroll in an orbital path. An axial thrust and anti-rotation assembly is mounted in the housing to limit the orbital scroll to orbital movement and to maintain the scrolls in proper relationship relative to each other.
The fixed scroll has an end plate, an involute wrap and a central discharge aperture. The orbital scroll has an end plate and an involute wrap. The fixed scroll is secured in the housing and the orbital scroll cooperates with the fixed scroll to form at least one pair of sealed fluid pockets.
The orbital scroll drive includes a crankshaft rotatably journaled in the housing. A crank pin portion of the crankshaft is connected to the orbital scroll to orbit the scroll in an orbital path. When the orbital scroll is driven in an orbital path, the sealed fluid pockets formed by the scroll wraps and end plates move toward the center of the scrolls, become smaller and compress the fluid they contain. The compressed fluid leaves the scrolls through the discharge aperture in the fixed scroll end plate and is discharged from the compressor housing through the fluid outlet.
The axial thrust and anti-rotation assembly axially positions the orbital scroll relative to the fixed scroll to keep the fluid pockets sealed and in conjunction with the axial tip seals, allow axial expansion of the scroll wraps that results from increased temperatures during operation. The axial thrust and anti-rotation assembly also prevents rotation of the orbital scroll while allowing generally circular orbital motion.
One common axial thrust and anti-rotation system includes a plurality of axial thrust balls positioned between a ball race on the front wall of the orbital scroll and a ball race mounted in the front section of the housing. A pair of rings with circular ball apertures are positioned between the ball races with the axial thrust balls in the circular ball apertures. One ring is attached to the housing and the other ring is attached to the orbital scroll. The circular ball apertures in both rings have a diameter, which allows the axial thrust balls to move in a circular orbit when the orbital scroll is driven in a circular orbit and which prevents rotation of the orbital scroll. Axial thrust and anti-rotation systems with axial thrust balls have a large number of parts, are somewhat difficult to assemble and require close manufacturing tolerances. They also require substantial axial space thereby increasing the length of the compressor. The point contact between the balls and flat surfaces of the ball races, may result in rapid wear if the parts are not properly hardened.
Oldham couplers are used to prevent rotation of orbital scrolls in relatively large stationary systems. These couplers are used in combination with complicated axial thrust structures for axially fixing the orbital scroll or the couplers include large heavy rings that require substantial space and are difficult to balance. Balancing is very important in vehicle applications where the compressor must be able to operate over a relatively large speed range.